Systems that transmit RF signals usually include an amplifier, followed by some passive structures as filters and switches that are connected via a matching circuit to an RF antenna. The impedances of the RF antenna and the amplifier should be matched to fifty Ohms in order to optimize the transmission of RF signals via the RF antenna and minimize the voltage standing wave ratio (VSWR) at the RF antenna.
Variable Matching circuit s might include variable capacitors (varactors) such as Gallium Arsenide (GaAs) varactors that provide change in their capacitance value according to an applied an input bias voltage. The GaAs varactor have a relatively limited capacitance range (the ratio between the maximal capacitance and the minimal capacitance of the GaAs varactor is usually less than four) and thus can perform an impedance match over a relatively limited impedance and frequency ranges.
Furthermore, because the GaAs varactor operates in the reversed-bias region, it should not receive an input voltage that will drive the GaAs varactor into the forward-bias region. As a result, the GaAs varactor should manage only an input voltage having a constant (DC) and variable components (AC) where the AC component has relatively limited voltage swing.
The GaAs varactor exhibits a non-linear relationship between its capacitance and the input bias voltage. It is desired to operate the GaAs varactor in a linear (or almost linear) region of operation to minimize non-linear distortions. FIG. 1 includes a graph 10 that represents the varactor non-linear relationship between the capacitance and the input bias voltage. Cmin 11 Cmax 12 are the minimal and maximal capacitances of the GaAs varactor. Vmin and Vmax 13 and 14 are minimal and maximal values of the input voltage and are designed to maintain the GaAs varactor in a reserved bias region. Curve 15 illustrates a maximal tolerable voltage swing of the input signal. The minimum peak voltage of the AC component VPMIN 16 should not exceed the junction potential required to bring the GaAs varactor into the forward region and the maximum peak voltage VPMAX 17 should be less than maximum allowed reverse voltage defined by the break-down voltage of the device.
In FIG. 1, the maximum allowed change in the operation point VBIAS 18 depends inversely on the peak-to-peak voltage swing across the varactor structure as the operation range of the varactor is limited by the maximum allowed forward and reverse bias conditions. Thus to provide a wide variable capacitance range, enabling the implementation of variable matching circuit s large impedance and frequency ranges, the AC component across the GaAs varactor should be minimized.
There is a growing need to provide system and method for impedance matching of RF systems over a relatively large impedance and frequency ranges and while managing signals of high voltage swing.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.